The iambic trimeter derives its name from its essential shape, which is three metrical units (hence trimeter) which are each basically iambic in form. The iambic metron has the following shape (where the x is an anceps, the - is a longum, and the u is a brevis):
Hence, reversing the current running though a wire will have the affect of reversing the direction of the magnetic force at a point some distance away from the wire. The affect that this has on the overall magnetic field depends on the shape of the wire.
The magnetic field lines generated around the wire due to the presence of the current are depicted in blue. To observe the direction of the field at any given point around the circumference of the wire, click and drag the compass needle, (its north pole red, its south pole blue).